An autopsy has been completed on a child who was found dead in a park swing as his mother pushed him, but the cause of death remains under investigation, police said Monday May 25.

Charles County Sheriff's Office spokeswoman Diane Richardson said that there were no findings on the cause or manner of death of the 3-year-old found on May 22 in La Plata, Maryland.

Richardson said further investigation and toxicology tests are needed. The 24-year-old mother was taken to a hospital. Richardson said she remained hospitalized Monday. Officials haven't identified her. They've said she may have been at the park for hours before the boy was discovered.

Richardson says detectives are working to establish a timeline of the days before his death. Previously, she said there were no obvious signs of foul play but that it hadn't been ruled out.

Meanwhile, a woman who identified herself as the child's maternal grandmother to a TV station, told the broadcast outlet that her daughter ordinarily "would never harm my grandson in any type of way."

Vontasha Simms also told WUSA-TV that her daughter had been diagnosed with a mental illness a few months ago and was seeking help. She didn't give specifics.

Police have not commented on details of the investigation or whether mental illness played a role.